The Theoretical Study Of The Hydrogen Bond Effects In Excited State Of Two Metal-organic Frameworks Material Systems

Metal Organic Frameworks material is constructed by organic linkers and metal ions(clusters) via coordinated-bond,which has plenty of O-H and N-H bonds, the inter-Ligand and intra-ligand hydrogen bond play a vital role of the constructions within these supramolecular crystal structure, what's more, have a great influential effect of the entire molecular structure and properties in the excited state.We do the research of energy transfer, electron transfer, and charge transfer of excited state; competitions between radiative transition and nonradiative transitions, to aim at realizing the relationship between Hydrogen bonds effect and luminescence properties, revealing the natural truth of excited state hydrogen bond.In the past years, most of the researches have been done on the hydrogen bond in the ground state. With the development of the experimental technology, the hydrogen bond in the excited state has become more and more interested by the scientists. To get better understand of the in the electronically excited state, diverse experimental and theoretical methods has been performed. Femtosecond time-resolved vibrational spectroscopy has shown potential to give a good insight into the microscopic dynamics and provided information on local structures. Time-dependent density functional theory (TDDFT) method has also been confirmed as a reliable method to investigate the hydrogen bond in the electronically excited state.In our work, the hydrogen bond and its effects in the excited state of hydrogen bonded complex molecular systems have been investigated by time-dependent density functional theory (TDDFT). For the [Cu(ipt)(dap)H2O]n·nH2O system, The calculated hydrogen bond lengths, the spectra shift of the stretching mode of the C=O and O-H group and the lengths of functional groups which form the hydrogen bonds in different electronic states confirmed the mechanism of the hydrogen bond strengthening in the electronically excited state,that means hydrogen bond 1:O1=H……C=O2 and hydrogen bond 2:O4-H……C=O3 are strengthened in the electronically excited state.Our theoretical study support the mechanism of the hydrogen bond strengthening made by Zhao et al.We found that the synergistic effect of the two hydrogen bonds of the Cu(H2BTC)(2,2-bipy) system contributed to stimulate the charge density transfer from the ligand to the metal in the excited state, which has been firstly proposed in the excited state dynamics of hydrogen bond. Meanwhile, the binding energy of the system in the excited state is significantly higher than the one in the ground state, indicating that the interaction between two monomers is strengthened, could well explain the non-local excited phenomenon. In addition, the dynamic changes of the two hydrogen bonds in the excited state will lead to the decrease of the hydrogen-bond energy levels in the excited state relative to the former Monomers, thereby reducing the probability of radiative inactivation and increasing non-radiative deactivation process. Therefore, we speculate that this hydrogen-bond Collaborative effect may facilitate the occurrence of the fluorescence quenching phenomenon,and there could be some relationships between the quenching phenomenon and the charge transfer from ligand to metal..